linux-kernel - Re: [PATCH v3 1/3] sched/fair: Move checking for nohz cpus after time check

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Message-ID: <4b8e64ef-8f7c-4978-91f3-a23bab109cc5@linux.ibm.com>
Date: Fri, 9 Jan 2026 20:44:18 +0530
From: Shrikanth Hegde <sshegde@...ux.ibm.com>
To: Peter Zijlstra <peterz@...radead.org>
Cc: mingo@...nel.org, vincent.guittot@...aro.org, linux-kernel@...r.kernel.org,
        kprateek.nayak@....com, juri.lelli@...hat.com, vschneid@...hat.com,
        tglx@...utronix.de, dietmar.eggemann@....com, anna-maria@...utronix.de,
        frederic@...nel.org, wangyang.guo@...el.com
Subject: Re: [PATCH v3 1/3] sched/fair: Move checking for nohz cpus after time
 check

Hi Peter. Thanks for going through.

On 1/8/26 6:14 PM, Peter Zijlstra wrote:
> On Wed, Jan 07, 2026 at 12:21:23PM +0530, Shrikanth Hegde wrote:
>> NOHZ idle load balancer is kicked off only after time check. So move
>> the atomic read after the time check to access it only when needed.
>>
>> When there are no idle CPUs(100% busy), even if the flag gets set to
>> NOHZ_STATS_KICK | NOHZ_NEXT_KICK, find_new_ilb will fail and
>> there will be no NOHZ idle balance. The current behaviour is retained.
>>
>> Note: This patch doesn't solve any cacheline overheads. No improvement
>> in performance apart from saving a few cycles of atomic_read.
> 
> Note that atomic_read() == READ_ONCE() is just a regular load, but sure.

Cool. thanks. Let me keep it in the series then.